Hawaiian Crabs Vanished When Humans Arrived

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Land crabs as large as an adult's hand once migrated between the
Pacific Ocean and the forests high on the Hawaiian islands. Their
disappearance may be the first documented extinction of a crab
during humans' presence on the planet, according to researchers.

Land crabs spend their adult lives in forests, and make risky
trips to the oceans to release their larvae, which grow into
crabs that return to land. The
most famous land crabs occupy Christmas Island, where they
make an arduous journey to the ocean every year.

Of the islands of the tropical Pacific, only Hawaii's seem to
lack these crabs. Now,
fossils have revealed that the crabs did indeed live there,
but like many other species they seem to have fallen victim to
changes wrought by humans.

Fossils left by the crabs predate the arrival of the Hawaiian
islands' first settlers, Polynesians who made the long trip by
sea around 1,000 to 1,500 years ago. After the time humans
arrived, the crab fossils rapidly disappeared.

The Hawaiian crabs, called Geograpsus severnsi, were
distinct from other land crabs in this part of the world; they
were large, lived farther inland and at higher elevations, and
had a diet that could include insects and young birds, according
to lead researcher Gustav Paulay, a marine malacology curator at
the Florida Museum of Natural History.

The first humans to arrive on these isolated islands destroyed
habitat, hunted native creatures and brought with them foreign
species, such as pigs, rats and dogs, which also preyed upon
native species, Paulay said. The later
arrival of Europeans in 1778 only worsened things for the
native species.

"The extinction crisis was huge and we have only an inkling what
it involved, because the fossil record is limited to only a few
kinds of organisms," he said. The other known victims include
many birds, such as flightless geese.